Carrier aggregation (CA) will be used in future 3GPP LTE wireless communication networks to provide improved data rates to users. Carrier aggregation includes transmitting data to or receiving data from user equipment (UE) on multiple carrier frequencies (component carriers). The wider bandwidth enables higher data rates.
A UE can generally be configured with a set of component carriers (CCs). Specifically, the UE is configured with a cell on each component carrier. Some of these cells may be activated. The activated cells can be used to send and receive data (i.e., the activated cells can be used for scheduling). The UE has up-to-date system information for all configured cells. Therefore, after a cell has been configured, it can be quickly activated. Thus, when there is a need for aggregating multiple CCs (e.g., upon the occurrence of a large burst of data), the network can activate configured cells on one or more of the CCs. Generally, there is a designated primary cell (Pcell) on a CC that is referred to as the primary CC, which is always activated. The other configured cells are referred to as Scells (and the corresponding CCs are referred to as secondary CCs).
The maintenance of a configured CC set in addition to an activated CC set enables battery conservation in the UE while providing CCs that can be activated when necessary, for example, when there is a substantial amount of data to be transmitted.
It is expected that multiple carriers will be activated only when there is a substantial amount of data to be transmitted. This implies that CCs will remain in the configured but deactivated state for extended time periods. It is essential to perform RRM measurements of cells on the deactivated CCs so that the appropriate CCs (and cells) can be activated. Performing measurements of multiple CCs requires the UE to operate its RF frontend at a higher bandwidth (in the case of intra-band aggregation), or to use an alternate transceiver for measurements. Both of these options cause significant power consumption in the UE. Performing frequent measurements of CCs with activated cells does not result in substantial additional power consumption since the UE is required to be able to receive control channels and data channels from the activated cells anyway (and therefore the RF front end needs to be able to receive the activated CCs). A UE is generally not expected to receive control and data channels on deactivated secondary cells. UEs are configured with secondary cells in the deactivated state for extended time periods. Cumulatively, measurements of cells on secondary CCs can consume large amounts of power. Thus it is generally considered beneficial to control the rate at which measurements of cells on secondary CCs are performed to minimize power consumption. That is, it is beneficial to perform measurements of cells on deactivated secondary CCs less frequently than measurements of cells on the primary CC and cells on activated secondary CCs.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.